Volume by disks, shells, or washers?

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The shell method is often but not always the most convenient.In summary, the easiest way to determine the appropriate method for finding the volume of a solid is to consider the function/functions that bound the region being revolved. The disk and washer methods are typically used for simple shapes, while the shell method is often more convenient for complex shapes. Ultimately, the best method will depend on the integral that needs to be evaluated.
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KMcFadden
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What is the easiest way to determine if the volume of a solid should be found by using disks, shells, or washers?
 
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Personally I always start with the shell method unless it is a really basic, simple shape(disk method)... But to answer ur question, I look for a hole. If there is one, then i am thinking washer, if there isn't and the solid is a very simple shape, then I go with the disk method. For the most complex shapes, i automatically go to the shell method.
 
  • #3
KMcFadden said:
What is the easiest way to determine if the volume of a solid should be found by using disks, shells, or washers?
There is no one-size-fits-all guidance here. It depends on the function/functions that bound the region being revolved. The disk and washer methods are essentially the same, with the washer method being used if the typical volume element is a disk with a hole in it.

Sometimes one method produces an integral that's easier to evaluate, and sometimes another method does.
 

1. What is the difference between volume by disks, shells, and washers?

Volume by disks, shells, and washers are all methods used to calculate the volume of a three-dimensional shape. The main difference between them is the shape of the cross-section used in the integration process. Volume by disks uses circular cross-sections, shells uses cylindrical cross-sections, and washers uses annular cross-sections.

2. When should I use volume by disks, shells, or washers?

The choice of method depends on the shape of the solid and the orientation of the axis of rotation. Volume by disks is best used when the shape has a defined height and a circular base. Shells are more suitable for shapes with a defined width and height, while washers are used when the shape has a hole or empty space within it.

3. How do I set up the integral for volume by disks, shells, or washers?

The integral for volume by disks is typically set up as ∫(base to top) πr² dx or dy, where r is the radius of the cross-section and x or y is the variable of integration. For shells, the integral is usually set up as ∫(left to right) 2πrh dx or dy, where h is the height of the cross-section. For washers, the integral is set up as ∫(inner radius to outer radius) π(R²-r²) dx or dy, where R is the outer radius and r is the inner radius of the cross-section.

4. Can volume by disks, shells, or washers be used for irregular shapes?

Yes, volume by disks, shells, and washers can be used for irregular shapes by breaking the shape into smaller sections and using the appropriate method for each section. This is known as the method of disks, shells, or washers by slicing.

5. What is the significance of using a larger number of disks, shells, or washers in the calculation?

The more disks, shells, or washers used in the calculation, the more accurate the result will be. This is because using a larger number of smaller cross-sections provides a better approximation of the shape of the solid. However, using too many cross-sections can be time-consuming and computationally intensive, so a balance should be struck between accuracy and efficiency.

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